• The Korean Journal of Rheology
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• v.11 no.2
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• pp.112-121
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• 1999

An MR(Magneto-Rheological) fluids damper is designed and applied to vibration suppression of a 1/4 car model. The damping constant of MR damper changes according to input current which is controlled in a semi-active way. Several control algorithms are compared in simulations and experiments. The advantage of the proposed Frequency shaped LQ control is that passenger comfort is emphasized in the range of 4~8Hz and driving safety is emphasized around the resonance frequency of unsprung mass.

• Journal of the Korean Institute of Intelligent Systems
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• v.15 no.2
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• pp.135-142
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• 2005

This paper presents an adaptive repetitive control scheme for optical disk drives to track a variable periodic reference signal. Periodic disturbances can be adequately attenuated using the concept of repetitive control, provided the period is known. Because optical disk drives support various speeds, they have the varying periodic disturbances. Based on repetitive control to change sampling frequency to follow the change of reference period, an adaptive repetitive control is proposed in order to deal with such disturbances. The proposed control consists of the repetitive controller and the frequency generator. The former uses a varying sampler operating at fixed multiple times of the disturbance frequency and the latter generates the changeable sampling frequency based on the disturbance frequency. The experimental results on the control of an optical disk drive demonstrate the effectiveness of the proposed schemes and the improvement of random access time as well.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.11a
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• pp.176-179
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• 2011

본 논문은 IEEE 802.11기반 무선 멀티홉 환경에서 은닉 노드가 존재할 때 전체 시스템의 효율 저하를 최소화 하면서도 평균 시간 지연 요구를 만족할 수 있는 경쟁 윈도우 제어 알고리즘을 제안한다. 이에 적용되는 최소 경쟁 윈도우 기준값을 주어진 topology에 따라 도출하고 각 트래픽 플로어의 QoS 요구조건 만족과 은닉노드가 존재할 경우에 성능개선을 위한 경쟁 윈도우 제어 패턴을 조절한다. 제안하는 경쟁 윈도우 제어 기법을 ns-2 시뮬레이션을 통해 검증하고, 모든 QoS 요구를 수용하면서 전체 성능 개선을 보이는 결과를 구하였다.

• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.53-54
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• 2007

이 논문에서는 구동기 용량제한을 갖는 선형시스템에 대한 저이득 추종 제어기 설계 문제를 다룬다. 주어진 시스템에 대한 추종 기준입력은 크기와 변화율에 제한을 갖는 시간에 따라 변화하는 일반적인 입력을 고려하며 제어기 설계 과정은 추종성능을 향상시키기 위한 2단계의 시스템 등가변환으로 구성된다. 먼저 제1단계에서는 잘 알려진 SVD(Singular Value Decomposition)의 원리를 활용하여 추종출력과 관련된 상태를 효율적으로 분리한 후 추종에러를 상태방정식 내에 포함하는 제2단계의 시스템 변환을 통하여 추종성능의 향상을 꾀한다. 제안된 추종 제어기의 설계 조건은 모두 LMI 형태로 표현 가능하며 잘 알려진 수치예제를 통하여 제안된 설계 기법의 효용성을 예시한다.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1923-1925
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• 2003

본 논문은 유리 기판과 실리콘 기판의 양극접합과 CMP공정을 통하여 정전기력으로 구동되는 마이크로 비틀림 액추에이터를 제작하고 이 제작된 액추에이터의 성능을 개선하는 방법과 실험에 관한 것이다. 이 비틀림 액추에이터는 미소 거울로 사용하기 위해 제작하였다. 미소 거울은 영상을 정확히 반사하거나 회절 시키는 것이 목적이지만 MEMS 공정의 특성 문제로 인해 일관적인 성능을 나타내는 것이 비교적 힘들다. 따라서 이를 개선하기 위해선 구조적인 접근 보다 실제 구동될 때의 현상을 보상하는 것이 필요하다. 일정한 입력전압에 비례하는 미소 거울의 변위를 알고 이를 기준으로 하여 시스템을 구동하여야 한다. 여기서 인가되는 전압에 비례하는 변위가 정확한지 측정을 해야 하고 만약 오차가 있다면 이를 개선하여야 한다. 또한 구동 시 발생하는 overshoot 현상과 작은 떨림 현상을 줄이고 빠른 시간 내에 응답하도록 시스템을 보상하여야 한다. 본 논문에선 PID 제어기법을 사용하여 $0.5^{\circ}$의 각도로 구동할 때를 기준으로 이 때의 구동전압 200V를 인가하고 오차를 측정하여 시스템을 보상하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.9 no.6
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• pp.591-597
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• 1999

When fuzzy logic controllers which are designed based on plant models and intuitive base are applied to real plants, the control systems may not give satisfactory control results due to the modeling error and the lack of knowledge on the plants. In that case. the controller must be retuned by adjusting the control parameters; this retuning process may require a large number of trial-and-error evaluations and thus much time and cost. In order to resolve these problems, we propose a systematic and efficient procedure for designing a fuzzy logic controller using response surface methodology. First wc select the initial optimal conditions of control parameters using a genetic algorithm, in which a nominal plant model with intrinsic modeling errors is used. And then we determine the tinal optimal conditions of the control parameters using response surface methodology. Computer simulations are performed to verify the capability of the proposed method.

• Journal of the Institute of Convergence Signal Processing
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• v.6 no.2
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• pp.95-99
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• 2005

This paper presents an accurate recovery method of the reference clock which is needed for network synchronization in two-way satellite multimedia systems compliant with DVB-RCS specification and which use closed loop method for burst synchronization. In these systems, the remote station transmits TDMA burst via return link. For burst synchronization, it obtains reference clock from program clock reference (PCR) defined by MPEG-2 system specification. The PCR is generated periodically at the hub system by sampling system clock which runs at 27MHz $\pm$ 30ppm. Since the reference clock is recovered by means of digital PLL(DPLL) using imprecise PCR values due to variable random jitter, the recovered clock frequency of remote station doesn't exactly match reference clock of hub station. We propose a robust recovery method of reference clock against random delay jitter The simulation results show that the recovery error is remarkably decreased from 5 clocks to 1 clock of 27MHz relative to the general DPLL recovery method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.129-135
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• 2008

The combined sewer overflows(COSs) which enters to river are involved with water pollution of rivers. Therefore, the standard capacity should be decided in proper standard considering water pollution density and characteristic of outflow. But in domestic, the standard capacity is not considered the characteristics of rainfall-outflows and is applied uniformly in all areas. The standard is triple of a maximum amount of sewage per one hour ; 3Q. The outflow of 3Q enters to sewage treatment plant and the overflows enter to river. In this study, a standard rainfall is estimated to determine the capacity of intercepting sewer by statistical analysis of rainfall data and it is considered about the regional characteristic of the rainfall-outflow. The standard rainfall is analyzed through the data of Seoul. In the result the standard rainfall was 6.76mm of 4hr duration. The rainfall-outflows and CSOs are analyzed using SWMM(Storm Water Management Model).

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.2223-2231
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• 2010

Recently, an important physical device of transportation, such as car, railroad, ship and aircraft has changed into electronic control unit. According to accident reports, the most of car accidents are caused by faults of embedded software loaded to computer control unit. The facts implies that the test to find defects in embedded software haven't performed sufficiently. As a result, it is necessary to establish the test procedures of embedded software based on safety assessment criteria. The objective of this proposal is to provide a unit test procedure complied with the safety assessment criteria for the embedded software. In addition, an effective unit testing procedure and defect analysis methods are proposed and a testing procedure using a safety criteria built-in tool is presented.

• Journal of Korea Society of Industrial Information Systems
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• v.10 no.2
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• pp.21-25
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• 2005

Human performance of system control under excessive mental-workload may differ from stable situation. In this study, design guidelines of secondary control system were introduced to enhance performance of safety control system. Under urgent situation, the first performance criterion is not a reaction time but safe control reaction that prevents system disaster. Therefore it is important to find out the facts that are mainly related system safety. Experimental results show performance of primary task didn't reflect whole system influence within a limited short reaction time. In this situation, the secondary task is more sensitive to system influence that varied with some factors of urgent status. Therefore, when a system proceeds to abnormal and unsafe status, and even more the reaction time is limited within a very short time to control the system, the estimation of human performance is more sensitive using secondary task performance then primary task performance. Those results mean it is required to develop various secondary tasks to design safety control systems preventing disaster, And also require many studies of estimation methods human performances especially when system status varies dangerous and/or unsafe situation.